The insect order Lepidoptera comprises the butterflies, moths, and skippers. They can be distinguished from all other insects by their two pairs of scale-covered wings. They undergo complete metamorphosis: eggs are laid, from which larvae hatch, and a pupal stage follows, during which the final adult form takes shape.

Lepidoptera are renowned for their sense of smell. The females of most species release complex, species-specific chemical compounds (pheromones), which can be detected by males from great distances. The males locate the females by following their scent plumes, often producing their own pheromones, which are used at close range during courtship. Some moths also have a well-developed sense of hearing, which has evolved as a method to detect the sonar of bats, which are important predators of moths. One group of moths, the tiger moths (Erebidae: Arctiinae) actually produce sound to interfere with the signals of bats or to advertise chemical protection gained from plant compounds.

For most Lepidoptera species, the vast majority of the life cycle is spent in the larval stage. Most larvae feed on living plant tissue, primarily leaves, but also flowers, buds, seeds, stems, roots, and bark. Some feed externally; others are miners or borers. A few species stimulate gall formation on their host plants. Many species are very host-specific; others feed on a wide variety of plant species. The larvae of some species feed on fungi or detritus, and a few have become facultative predators or parasites. Most adult Lepidoptera live for only 1 or 2 weeks, and have a fairly specific flight period. Most adults feed on nectar, but many have atrophied mouthparts and do not feed at all, living on the fat reserves built up in the larval stage. Many species, particularly butterflies, are known to “puddle” at damp places, presumably to obtain dissolved minerals.

The Lepidoptera form an essential part of most terrestrial ecosystems. As herbivores, they help to regulate plant growth (through herbivory and nutrient cycling) and when their population levels are high they can act as agents of plant community succession. Many adult lepidopterans are important pollinators. Larvae and adults are major food sources for many other animals, including songbirds, bats, and other insects.

A few species of Lepidoptera are such good resource competitors with humans that they are considered pests. Although the proportion of species in this category is very small, it includes pests of food crops, trees and timber, and stored food products. Although only two moth species have larvae that eat silk and wool products, this extremely rare feeding habit is often misattributed to the whole group by the uninformed. Silk itself comes from human exploitation of the Silk Moth, Bombyx mori (Linnaeus).